Field of the Invention
The present invention relates to a fixture for a machine and, more particularly, to a positioning block structure for a machining fixture which obtains machining precision and prolongs using lifespans.
Description of the Prior Art
Conventional machining fixtures are designed to satisfy various machining requirements. For example, a common machining fixture contains a base and a workpiece holder. The base is mounted on a machine, and the workpiece holder is applied to position a workpiece which will be machined. The workpiece holder is connected with or removed from the base, such that after the workpiece is machined, it is removed from the base with the workpiece which is machined. Thereafter, another workpiece holder, on which anther workpiece is mounted, is fixed on the machine, thus decreasing replacement waiting time and increasing machining efficiency. To connect the workpiece holder on the base quickly, a structure is configured between the base of the machining fixture and the workpiece holder. Generally speaking, a plurality of positioning blocks is symmetrically arranged on the base, and plural mounting grooves are defined on the workpiece holder for engaging with the plurality of positioning blocks, thus aligning the plurality of positioning blocks with the plural mounting grooves accurately.
With reference to FIG. 11, a conventional machining fixture contains a base 10 and a workpiece holder 20. The base 10 includes a first connecting face 101 on which plural first fixing faces 102 and plural positioning blocks 103 are formed. Each positioning block 103 is one-piece formed on the first connecting face 101. The workpiece holder 20 is connected with or removed from the base 10 and includes a second connecting face 201 on which plural second fixing faces 202 and plural fixing slots 203 are defined. When the workpiece holder 20 is in connection with the base 10, the plural second fixing faces 202 contact with the plural first fixing faces 102 of the base 10, and the plural fixing slots 203 engage with the plural positioning blocks 103 of the base 10, thus connecting the workpiece holder 20 with the base 10 accurately. However, the plural positioning blocks 103 are one-piece formed on the base 10 to cause difficult machining and high production costs.
Referring further to FIG. 12, a fixture for electrical discharge machining contains a base 30, a plurality of positioning blocks 40, and a workpiece holder 50. The base 30 includes a first connecting face 301 on which plural first fixing faces 302 and plural tapered fixing slots 303 are formed. Each tapered fixing slot 303 has a threaded hole 304 defined on a bottom end thereof. Since each positioning block 40 is an independent component, it is manufactured difficultly at a high cost. Each positioning block 40 is a circular bar or in a strap shape and has a through orifice 401 formed on a middle section thereof. A screw bolt 402 is screwed with the threaded hole 304 of each tapered fixing slot 303 of the base 30 via the through orifice 401 of each positioning block 40, such that each positioning block 40 enters into and contacts with each tapered fixing slot 303. The workpiece holder 50 is connected with or removed from the base 30 and includes a second connecting face 501 on which plural second fixing faces 502 and plural locating slots 503 are arranged. When the workpiece holder 50 is connected with the base 30, the plural second fixing faces 502 contact with the plural first fixing faces 302 of the base 30, and the plural locating slots 503 engage with the plurality of positioning blocks 40 on the base 30, thus connecting the workpiece holder 50 with the base 30 exactly. Nevertheless, the plural first fixing faces 302 of the base 30 and the plural second fixing faces 502 of the workpiece holder 50 are broken or worn easily in a machining process to cause a rough surface. Thus, the base 30 and the workpiece holder 50 are trimmed flatly, and a height of each first fixing face 302 of the base 30 and each second fixing face 502 of the workpiece holder 50 is reduced. Accordingly, when each locating slot 503 of the workpiece holder 50 engages with each positioning block 40 on the base 30, each second fixing face 502 does not contact with each first fixing faces 302 of the base 30 completely (i.e., a gap generates between each second fixing face 502 and each first fixing faces 302), the workpiece holder 50 does not connect with the base 30 stably, and a machining precision of the machine and a lifespan of the machining fixture decrease.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.